This invention relates to power generating systems, and in particular, to such systems employing geothermally heated fluid.
One of the dark clouds hovering over the economic future of mankind is the fact that the known resources of fossil fuels are being depleted at a relatively rapid rate. In fact, it is estimated that such known resources will be depleted sometime during the twenty-first century if current growth rates are continued. Vast sums of money are being invested in research by the industrial nations to develop alternative sources of energy.
In searching for new sources of energy, one of the chief desirable characteristics for such new source is that such source be of a non-polluting type. For example, the utilization of nuclear energy has been partially limited by the fear of radiation pollution affecting the nearby populous. In addition, there is a further fear of thermal pollution of the streams, lakes or rivers used as the heat sink for the nuclear generating plants.
A potential source of non-polluting energy is the development and utilization of geothermal heat. Currently, in several parts of the world, for example, Northern California, Italy, and Japan, geothermal fluids are employed as the source of energy for the generation of power. The geothermal fields thus employed have been frequently referred to as "dry steam" fields. That is to say, the geothermal fluid in the fields at the wellhead is steam rather than liquid water. Heretofore, it has been the practice to develop only the dry steam fields as the geothermal steam may be directly employed to drive a vapor driven turbine.
Liquid dominated geothermal fields are about twenty times as abundant as dry steam fields. However, such liquid dominated fields have not been developed as extensively as is desirable for several reasons. First, the geothermal fluid, when in its liquid phase, is quite corrosive and includes much particulate matter entrained therein. Accordingly, it has been the practice to separate the geothermal water from the geothermal steam and to only employ the steam to produce power. The cost of separating the steam from the water constituent of the geothermal fluid has increased the initial cost and complexity of providing the geothermal generating system. In addition, the efficiency of such systems wherein only a small portion of the available fluid is used is not very high.
Many systems have been proposed to indirectly employ the geothermal fluid to heat a working fluid, for example isobutane, which is then directly employed to drive a tubine. An example of a system of this type is disclosed in U.S. Pat. No. 3,795,103, issued Mar. 5, 1974. U.S. Pat. No. 3,751,673, issued Aug. 7, 1973, is illustrative of another type of system whereby the geothermal fluid is directed through a helical screw expander so that the water constituent of the fluid is flashed to steam to drive a generator coupled to the fluid expander.
The present invention relates to a system employing geothermal fluid as the source of energy having improved efficiency whereby substantially all of the energy from the geothermal wells may be utilized.